it's a fine question for jquery noobs such as myself. I cobbled together some jquery pages by cutting and pasting from the internet, and it was the first question I had about what I was doing.
–
Mark HarrisonJun 27 '09 at 3:40

Some JavaScript libraries uses $ too (example: prototype). To avoid conflict with those other libraries jQuery provides jQuery.noConflict() function. Calling this function the control of the $ variable goes back to the other library that first implemented it. Doing this to use jQuery you can't do this $('div.someClass') anymore, instead jQuery('div.someClass').

Alternatively can do this:

jQuery.noConflict();
jQuery.ready(function($) {
// use $ for jQuery
}
//use $ for the other library

When writing plugins to avoid problems with the usage of noConflict you can pass 'jQuery' to a function:

Strange but true, you can use "$" as a function name in JavaScript. It is shorthand for jQuery(). Which you can use if you want. jQuery can be ran in compatibility mode if another library is using the $ already. Just use jQuery.noConflict(). $ is pretty commonly used as a selector function in JS.

In jQuery the $ function does much more than select things though.

You can pass it a selector to get a
collection of matching elements from the DOM.

You can pass
it a function to run when the
document is ready (similar to
body.onload() but better).

You can pass it a string of HTML to turn
into a DOM element which you can
then inject into the document.

You can pass it a DOM element or
elements that you want to wrap with
the jQuery object.